It is generally known that one of the problems encountered in producing a two-component thread is the avoidance of winding into the bobbin the final thread when one of its two components is lacking for some reason.
This problem is solved, as a rule, by ensuring forced servering or breaking of the remaining other component of the two-component thread when the feed of the first component, which may be either one of the two, ceases, and this involves monitoring the presence of both components of the thread prior to their twisting together with aid of various techniques and devices. The most popular approach is monitoring by direct contact, i.e., by physically feeling each one of the components of the thread by means of various kinds of feelers or sensors.
However, this monitoring technique is feasible only in case of such types of two-components thread whose components allow for their physical feeling in direct contact with the feelers, i.e., have adequate relative strength and tension, which is the case of, for example, twisted threads or yarns.
There is also in existence another monitoring technique, namely, that of monitoring the thickness of the final thread after the twisting together of the components, when sudden thinning of the final thread is considered a proof of distruption of the normal process of production of the thread, and used as a signal for actuating corresponding mechanisms. This technique is the obvious choice in case of two-component thread types where the twisted- or wound-around component is separated fibers that would not be physically contacted by a feeler.
The simplest devices embodying this technique are those employing the principle of go and no-go gages. A device of this kind normally includes an element engaged by the running thread and having a slit whose width is greater than the thickness of a single component of the thread, but short of the thickness of the final thread. Should either one of the components of the two-component thread become broken or its supply exhausted, the other component slips into the slit, which serves as a signal of disruption of the normal production process.
Efficient and reliable performance of devices of the above-described kind, however, can be ensured only when the ratio of the thickness of one of the components to that of the final thread is as small as 1:5 to 1:10, or even smaller.
Various devices are known employing the abovedescribed go/no-go gage principle. These devices in most cases incorporate a complex system of transmitting a signal of disruption of the production process to actuating members, these actuating members themselves being also quite complicated. Furthermore, the considerable distance from the location of the pickup with its feeler or gage to the spot where the remaining component is forcedly broken or severed results in an increased amount of waste in the form of a single thread and complicates the procedure of making good the breakage, as the remaining single component of the thread is wound into the final bobbin and requires subsequent removal.
There is known an apparatus for producing twocomponent thread (cf. SU Inventor's Certificate No. 706,473; Int.Cl..sup.2 DO1H 13/16, dated 1979) comprising a twisting member, a holder of a package with one component of the two-component thread, means for feeding the other component of the two-component thread into the twisting member, a unit for winding the two-component thread, including a package holder having an axle for its rotation, and a device for severing one of the components of the two-component thread when the feed of the other component thereof ceases, arranged intermediate the twisting member and the winding unit and including an element adapted to engage the two-component thread, having a slit of a width which is short of the thickness of the two-component thread and in excess of the thickness of one of the components of the two-component thread.
In the apparatus being described the twisting member includes the hollow spindle of a spinning-cum-twisting machine, and the device for severing the remaining component of the two-component thread in the absence of the other component, including a slit-type thread guide underlying the spindle, a deflecting wire offset from the axis of the spindle, and a bush secured to the bottom part of the spindle, for winding thereonto and breaking the component of the two-component thread that has passed through the slit-type thread guide in the absence of the other component.
In this apparatus the forced breaking of one of the components of the two-component thread is provided for by a bush of a simple design, and effected by overtensioning this component of the thread by the action of the winding unit, the breaking taking place practically at the same point where the flaw is detected, so that no defective yarn is wound into the bobbin with the final thread, and no time is wasted on its subsequent removal.
However, the winding of the component of the thread to be broken onto the bush rotating with the spindle brings about undesirable consequences. Firstly, it complicates the operation and affects the productivity, involving as it does subsesquent arresting of the spindle for cleaning the bush from the wound yarn; secondly, when the component of the thread is relatively strong, e.g., made of synthetic fiber, its tensioning aside from the axis of the spindle applies a considerable lateral load to the bearings of the spindle, thus stepping up their wear and curtailing their service life. Finally, the yarn wound onto the bush goes to waste, which increases the input of the components of the two-component thread and reduces the yield of the final thread.